在Swift中结束CAEmitterLayer的正确方法是什么？

Question

我几乎在Swift中看到了连续发射器的示例，并且在Obj-C中找到了一个示例，方法是将发射器单元的birthRate设置为0.0，但是它似乎不起作用，所以我一定做错了。在我的示例中，我可以看到一条消息，将出生率设置为0十六倍，但是粒子继续不断流动。

@IBAction func particleBtnAction(_ sender: Any) {

    let emitter = CAEmitterLayer()
    emitter.emitterPosition = CGPoint(x: self.view.frame.size.width / 2, y: -10)
    emitter.emitterShape = kCAEmitterLayerLine
    emitter.emitterSize = CGSize(width: self.view.frame.size.width, height: 2.0)
    emitter.emitterCells = generateEmitterCells()
    self.view.layer.addSublayer(emitter)

    // perform selector after 1.5 seconds when particles start
    perform(#selector(endParticles), with: emitter, afterDelay: 1.5)

}

private func generateEmitterCells() -> [CAEmitterCell] {

    var cells:[CAEmitterCell] = [CAEmitterCell]()
    for index in 0..<16 {
        let cell = CAEmitterCell()
        cell.birthRate = 4.0
        cell.lifetime = 1.0
        cell.lifetimeRange = 0
        cell.velocity = 0.7
        cell.velocityRange = 0
        cell.emissionLongitude = CGFloat(Double.pi)
        cell.emissionRange = 0.5
        cell.spin = 3.5
        cell.spinRange = 0
        cell.scaleRange = 0.25
        cell.scale = 0.1
        cells.append(cell)
    }
    return cells
}

@objc func endParticles(emitterLayer:CAEmitterLayer) {

    for emitterCell in emitterLayer.emitterCells! {
        emitterCell.birthRate = 0.0
        print("birth rate set to 0")
    }

}

Answer 1

设置CAEmitterLayer的lifetime零停止任何新的emitterCells发射存在：

@objc func endParticles(emitterLayer:CAEmitterLayer) {
    emitterLayer.lifetime = 0.0
}

Answer 2

您可以使用关键路径为每个单元格分配名称并循环它们，当您想要更改它们时更改每个单元格的属性：

private func generateEmitterCells() -> [CAEmitterCell] {

    var cells:[CAEmitterCell] = [CAEmitterCell]()
    for index in 0..<16 {
        let cell = CAEmitterCell()
        cell.birthRate = 4.0
        cell.lifetime = 1.0
        cell.lifetimeRange = 0
        cell.velocity = 0.7
        cell.velocityRange = 0
        cell.emissionLongitude = CGFloat(Double.pi)
        cell.emissionRange = 0.5
        cell.spin = 3.5
        cell.spinRange = 0
        cell.scaleRange = 0.25
        cell.scale = 0.1
        cell.name = "cell\(index)" // cell name
        cells.append(cell)
    }
    return cells
}

@objc func endParticles(emitterLayer:CAEmitterLayer) {

    for i in 0..<(emitterLayer.emitterCells?.count ?? 0){

        emitterLayer.setValue(0.0, forKeyPath: "emitterCells.cell\(i).birthRate")
        print("birth rate set to 0")

    }

}